1. Field of the Invention
This invention relates to scroll type fluid displacement apparatus, and has particular application in scroll type compressor systems.
2. Description of Prior Art
Scroll type fluid displacement systems, including pumps, compressors and expanders, have become generally well-known and are extensively described in patent and technical literature. A rather extensive discussion, for example, of such prior art relating to such devices is seen in U.S. Pat. No. 3,884,599, which patent also describes the operating principle of scroll fluid displacement systems. Other patents can be seen which disclose other improvements in scroll devices. One example of the latter is U.S. Pat. No. 4,082,484 which describes a drive shaft arrangement for a scroll fluid displacement device, the drive shaft having a fixed crank connected to the orbiting scroll and a counterweight for dynamically balancing the eccentric loads imposed by the orbiting scroll apparatus. Another patent, U.S. Pat. No. 4,259,043, describes a combined thrust bearing/coupling for maintaining a predetermined angular relationship between an orbiting and fixed scroll wrap of a scroll type fluid displacement system. Numerous other patents could be mentioned along these lines, but the foregoing patents have particular relevancy insofar as the inventive concept herein presented is concerned.
As regards the present invention, a problem yet to be solved in scroll devices is how to reduce the mass of the orbiting structure while still strictly maintaining axial tip clearances between the wraps. Since reducing the mass of the orbiting wrap, for example, as well as of its supporting base plate, normally results in a less rigid structure, axial bending loads imposed on the base plate can result in their deformation with the consequent axial displacement of the involute wraps which produces tip sealing and leakage problems. It has been observed that axial restraint against such displacement is desirable, particularly in the central region of the orbiting wrap assembly when the device in question is a compressor having a central fluid outlet, since higher pressures are encountered in the outlet region of the wraps as opposed to the outer areas which are arranged to intake pumped fluid. This is not to say that the outer area of the base plate carrying the orbiting wrap can be ignored in terms of axial restraint, since a sealing ring cooperating with the base plate is normally provided at the peripheral area of the latter to isolate the intake chamber or area of the compressor from the remainder of the housing containing the orbiting wrap assembly. Indeed, an axial restraint arrangement along these lines is shown in the above-mentioned U.S. Pat. No. 4,082,484 which relates to a scroll compressor and describes an axial restraint including a centrally located thrust bearing and a peripherally located anti-rotation Oldham-type coupling. However, the orbiting plate constructed in accordance with such prior art teachings was usually designed to be rather rigid in an axial sense whereby the central thrust bearing was able to react virtually all of the axial loadings between the orbiting base plate and the drive shaft, while the peripheral coupling, which did not include any bearing elements in the conventional sense, essentially performed the function of maintaining the orbiting wrap in predetermined angular relationship with the stationary wrap. Thus, there still remained the problem of axially restraining a lightweight, less rigid base plate and orbiting wrap assembly against axial displacement across its full diameter, without incurring excessive friction and wear problems and while maintaining the system within a compact outer envelope. The present invention is intended to solve this problem.
Yet another problem encountered with prior art scroll fluid displacement devices operating as compressors, particularly where the compressor must work with inlet fluids comprising a mixture of gas and liquid phase components, (e.g., refrigerant compressors) is to minimize intake of liquid phase fluid into the fluid displacement chamber(s) between the fixed and orbiting wraps. While the prior art generally can be shown to provide numerous illustrations of how such liquid and gas phase components can be separated, none has been noted as providing a simple solution that can be incorporated directly in the inlet of a scroll type fluid compressor. The present invention is intended to provide a solution to such problem.
Still another problem in prior art scroll compressor devices has been the maintenance of uniform scroll tip clearances when the scroll is subjected to thermal gradients between the central and outer areas of the scroll wraps. This problem can be particularly severe when axially longer wraps are used, since the total thermal expansion of such wraps is greater than in the case of shorter wrap lengths. The present invention contemplates a solution to this problem by preforming the wraps to take into account their differential expansion between their inner and outer areas.
This invention furthermore contemplates a refinement to the shape of a counterweight mass commonly provided on drive shafts of orbiting scroll apparatus to dynamically balance the eccentric loads applied by the orbiting scroll system. In prior art devices, there is a tendency for the centers of gravity of the orbiting scroll and the counteweight to be axially offset, creating bending and shear loading in the drive shaft system and other imbalances. The present invention is intended to provide a counterweight that is configured to avoid undue separation of the center of gravity of the orbiting plate and the center of gravity of the counterweight, despite the presence of the reinforcing ribs between the orbiting plate and the counterweight.